This invention relates to the construction of motor vehicles, and more particularly to the construction of cargo vehicles having a low profile and including a self-storing ramp for loading and unloading.
Cargo vehicles, including conventional cab, chassis, and van combinations, are used for a variety of applications, including pick-up and delivery of commercial packages and transportation of household goods. In these and other applications, the vehicles are often loaded and unloaded at facilities which are not equipped with a traditional loading dock having a floor level even with the floor level of the cargo section of the vehicle. The vehicle loading and unloading locations also typically lack power-assisted loading equipment, such as lift trucks and the like. Hence, loading and unloading of such vehicles is often performed manually. It is therefore highly desirable to construct cargo vehicles having features which minimize the amount of human effort required to load the vehicle.
One way manufacturers of prior art cargo vehicles have addressed this problem is by providing a loading ramp to extend from the floor of the cargo area at the rear of the vehicle to the ground. Personnel may carry items up the ramp more easily than lifting the item from the ground to the cargo compartment. The ramp also permits loading via a wheeled hand-truck or similar loading aid.
For vehicles which are equipped with loading ramps, it is preferable that the vehicle provide a place where the ramp may be stored when not in use, such as when the vehicle is being driven from one location to another. The ramp storage space is preferably provided without reducing the space available for cargo storage.
Many cargo vehicles are constructed by assembling a van body onto a commercially available vehicle chassis. The chassis typically has a pair of structural members, referred to as chassis frame rails, which are arranged in spaced parallel relation to each other and extend longitudinally from a position near the front of the vehicle to the rear of the cargo section of the van. The rails each have flanges at their top and bottom ends. The flanges on each rail extend inward toward the opposite rail, giving the cross-section of the chassis frame rails a squared-off "C"-shaped appearance. The vehicle body is mounted on the vehicle chassis. A body longitudinal rail, similar to the chassis frame rails, is mounted atop each of the chassis frame rails to support the cargo section floor. The chassis frame rails and body longitudinal rails are separated by wooden "breaker" strips having a thickness of several inches which reduce the propagation of shock and vibration from the chassis rails to the body rails. A large number of "cross sill" structural members are mounted on top of and perpendicular to the body longitudinal rails. The cargo section floor, composed of a large number of wooden boards, are secured on top of the cross sills.
Some manufacturers of such prior-art cargo vehicles have found the space between the chassis frame rails to be an ideal location for storing the loading ramp. The ram width is selected so that it is narrow enough that the ramp fits between the chassis frame rails but wide enough that the ramp remains captured by the inward-extending rail flanges.
Another way to minimize the human effort in loading and unloading a vehicle is to reduce the height of the floor of the cargo section. The energy required to raise an object is proportional to the distance it is to be raised. Commercial vehicle chassis manufacturers have developed "low-profile" designs in which the height above ground of the chassis frame rails is reduced. Since the chassis frame rails support the cargo section of the vehicle, for a given body design, lowering the chassis frame rails advantageously lowers the height of the cargo section floor. Use of a low-profile chassis also makes the vehicle easier to drive, especially for inexperienced drivers.
For some vehicles, however, lowering the chassis frame rails precludes storage of the ramp between the rails, because the clearance between the rails and the vehicle drive train is also reduced. As a result, during some driving conditions, drive train components, such as the differential housing, may intrude into the space between the chassis frame rails. For longer vehicles, the differential is positioned far forward, such that the ramp in its storage position does not extend into the region into which the differential intrudes. For shorter vehicles, however, the ramp may extend forward beyond the differential, so that when driving on an uneven surface, the differential may collide with the ramp. Using a substantially shorter ramp is not an effective solution to the problem, because the greater inclined slope produced by the shorter ramp is unacceptable to users. For most applications, ramp lengths shorter than about ten feet are not desirable.
In addition to the ramp storage problems, the use of existing van bodies with the commercially available low-profile vehicle chassis does not provide as great a reduction in the cargo section floor height as is desirable by vehicle users and fleet operators.